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Here's one you can make yourself

Hands up those of you who know what a spectrophotometer is? Hmmm, thought so. Anyway, for those who don't, it's a jolly useful bit of kit that can analyse the spectral composition of light and show you how much of each wavelength is present. You can get ones that hook up to a computer and, with the right software, will display rather fetchingly-colourful spectragraphs.

If you pointed one at a sodium street lamp, you would get a peak in the yellow part of the spectrum. Such devices are now much more affordable than they used to be, in that not long ago a spectrophotometer would have cost more than my car (OK, my car is a three-and-a half-year-old Nissan MPV that is inexplicably less popular than its unreliable rivals, but you get my drift).

You can produce your own spectragraph for next to nothing. First, use some card, glue and an old DVD to make a device that splits a light source into a spectrum. Next, grab a digital camera or cameraphone to photograph said spectrum. Having transferred this image to a computer, fire up a fabulous free piece of software called tracker.jar to make the graph.

Finally, if you must, colour it in. There, that last bit got the geographers' attention. You know where to call for further details - or to complain about the pathetic stereotyping of another subject.

The homemade spectrograph sounds like something out of Blue Peter. In this case, I don't think that is a bad thing. I feel passionately that there is a need for equipment for excellence in science departments, but the homemade device has an advantage. Commercial spectrophotometers are black boxes. Kids can hook them up to laptops, point a fibre-optic probe at a light source (note how physicists can't simply say "light") and out pops a spectrograph.

How does it work? Dinnae ken. At least the sticky-backed plastic version lays it all bare. The science world is full of mysterious boxes with probes and displays. Making your own instrument can be a cracking learning experience.

It's even better if, having made and tested it, you can then get to use a proper one that looks as modern as something you'd find in a business studies department.

Gregor Steele knows of a good experiment with a spectro-photometer, some coloured lights and two ping-pong balls.

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